Typical asphalt shingles have granules embedded in an outward-facing side of the product. Among other benefits, the upper surface of shingles is granular to provide UV resistance, ensuring a long service life. The non-granular underside of most asphalt shingles, including field and starter shingles, consists essentially of an adhesive mass, which is typically embedded into a scrim or mat.
Asphalt shingles are often cut using a straight utility knife blade by scoring the non-granule side of the shingle. Another method of cutting asphalt shingles on the non-granule side is using a hook blade installed into a utility knife. This permits the roofer to cut the shingles at a single point of contact on the knife blade, with the roofer facing the granular shingle side. Hook blades are commonly used along rake edges when a shingle needs to be cut to length, such as when the shingle extends past a drip edge and into transitions, such as in a valley area.
The act of cutting shingles on the non-granular side, although preferred and often easier, is not always possible, sometimes due to job site requirements, or preferred. For example, many roofers cut their books of starter shingles with the granule side facing the roofer.
Furthermore, field shingles, to prevent seams of subsequent courses from lining up, which may cause leaks, are typically cut, starting from a corner of a roof, in a shape resembling a ladder. The ladder effect of field shingles coming off the rake requires approximately 90% of the field shingles be cut to length at the rake location. Because of this, the roofer is often forced to look at the exposed granular side of the shingle determine where to cut the shingle. Also, the prevalence of laminate, i.e. dimensional, shingles also can force the roofer to look at the exposed granular side of the shingle to determine where the shingle is not laminated, i.e. of single thickness, as standard hook blades struggle with cutting these shingles at the laminate, especially in colder weather. In such situations, it is typical for the roofer to cut the shingle on the granule-containing side.
The typical roofing hook blade, as shown in FIG. 1, fits into a utility knife and is approximately 0.025″ thick 201, 2¼″ long 202, and ¾″ wide 203. Hook blades also typically comprise a means of engaging 204 a handle, to both allow the blade to be retained by and prevent the blade from disengaging from the handle during use. The base 205 leads to a flat angle 206 of approximately 45 degrees. The flat angle 206 continues for approximately ⅜″ and becomes a sharpened edge 207, which continues to the point 208. The point 208 is typically in line with the base 205, as depicted by the imaginary line 209. The sharpened edge 207 is typically a semi-circle or continuous arch 210.
Where a roofer uses a typical hook blade, the flat angle 206 forces the roofer to hold the knife upright, reducing the force that can be easily applied to the roofing product, as the roofer must apply force to the knife to maintain this upright position while pulling on the knife in the direction of the cut tends to pull the knife away from this upright position. For at least this reason, the closer the utility knife is to the flat plane of the product being cut, the easier it is to pull the knife through the material. Also, when drawing the knife to apply maximum force, an upright position effectively shortens the hook on the blade, making it difficult to cut through laminate shingles in an ergonomic manner.
Additionally, a typical hook blade results in only a single point of contact 211 between the blade and the shingle, due to the limited way the knife must be drawn. This causes the blade to wear out quickly at the single point of contact 211, requiring frequent blade replacement, despite the majority of the blade retaining a sharp edge.
Furthermore, typical hook blades, due to their narrow point 208, are prone to breakage as the roofer applies lateral pressure when rotating the blade or cutting a shingle along an object, such as a drip edge.
Lastly, typical hook blades are problematic because there is no way to control how deep the blade cuts. Many products in the roofing industry come in roll form, including tar paper, synthetic underlayment, and self-adhered products and cover materials, such as, TPO, EPDM, and modified bitumen. The point 208 on a standard hook blade is prone to cutting the underlying rolled product, as there is no way to regulate the blade's depth with the product needing to be unrolled prior to cutting.
Therefore, what is needed is a blade configured to cut a roofing shingle from the underside, using more than one point of contact on the blade, and that can withstand lateral forces encountered during roofing-related cutting without breakage that also incorporates a means of limiting the depth of cut.